Impairments of Lexical-Semantic Processing in Aphasia: Evidence from the Processing of Lexical Ambiguities

Abstract

Broca's and Wernicke's aphasics performed speeded lexical decisions on the third member of auditorily presented triplets consisting of two word primes followed by either a word or a nonword. In three of the four priming conditions, the second prime was a homonym with two unrelated meanings. The relation of the first prime and the target with the two meanings of the homonym was manipulated in the different priming conditions. The two readings of the ambiguous words either shared their grammatical form class (noun-noun ambiguities) or not (noun-verb ambiguities). The silent intervals between the members of the triplets were varied between 100, 500, and 1250 msec. Priming at the shortest interval is mainly attributed to automatic lexical processing, and priming at the longest interval is mainly due to forms of controlled lexical processing. For both Broca's and Wernicke's aphasics overall priming effects were obtained at ISIs of 100 and 500 msec, but not at an ISI of 1250 msec. This pattern of results is consistent with the view that both types of aphasics can automatically access the semantic lexicon, but might be impaired in integrating lexical-semantic information into the context. Broca's aphasics showed a specific impairment in selecting the contextually appropriate reading of noun-verb ambiguities, which is suggested to result from a failure either in the on-line morphological parsing of complex word forms into a stem and an inflection or in the on-line exploitation of the syntactic implications of the inflectional suffix. In a final experiment patients were asked to explicitly judge the semantic relations between a subset of the primes that were used in the lexical decision study. Wernicke's aphasics performed worse than both Broca's aphasics and normal controls, indicating a specific impairment for these patients in consciously operating on automatically accessed lexical-semantic information. ® 1993 Academic Press. Inc. This research was supported by a stipend from the Max-Planck-Gesellschaft zur Forderung der Wissenschaften. I thank Colin Brown, Pienie Zwitserlood, and two anonymous reviewers for their helpful comments on an earlier version of this article. Address reprint requests to Peter Hagoort,

The Influence of Neighborhood Density on Phonetic Categorization in Aphasia

“…While Pitt and Samuel (1993) revealed several sources of variation in studies that have examined the lexical influence on phonetic identification, the present investigation demonstrated that neighborhood density is also an important factor ta control in the design of phonetic identification continua (see also Newman et al, in press). The emergence of neighborhood density effects for aphasie patients also provides support for the contention that lexical aeeess deficits in these subjects are nat the praduct of a disturbance in the lexical base of information, but result from 97 deficits in the processes involved in retrieving and acting upon this information (Hagoort, 1993;Milberg et aL, 1987). While previous research has suggested that nonfluent aphasies may show a greater reliance on heuristie strategies in language processing than fluent aphasies or normals Blumstein et al f 1994;Milberg et aL, 1995), the results of the current study are someYlhat ambiguous in terms of the relative dependencies of aphasie subjects on higher-Ievel sources of information in phonetic pracessing.…”

“…Hagoort (1993) has previously suggested that the activation levels of lexical items decay more rapidly for aphasie subjects as compared ta normal subjects. Thus, il is possible that the activation of 'NOrd endpoints in Experiment 1 was only strong enough in the fast range ta influence the fluent and nonfluent aphasie subjects' phonetie judgements but had decayed by the intermediate and slow RT ranges.…”

“…That is, it is possible that what has previously been interpreted as a deficit in the automatic spread of activation may rather be a more rapid decay in the activation levels of related lexical items in nonfluent aphasies as compared to normals (cf. Hagoort, 1993). The CUITent study, which examines the response patterns of subjects by reaction time range, may be able to tap the rates of activation and inhibition of lexically-related items more clearly than lexical deeision studies which use reaction time as a depandent variable.…”

Hemispheric Contributions to Lexical Ambiguity Resolution: Evidence from Individuals with Complex Language Impairment Following Left-Hemisphere Lesions

“…In normals, the influence of a single word context on lexical ambiguity processing has been equivocal, with reports of selective meaning activation in self-paced tasks which, by their nature, do not rule out the possibility of previous multiple lexical access (e.g., Balota & Duchek, 1991;Schvaneveldt, Meyer, & Becker, 1976) and findings of multiple meaning activation under certain conditions and paradigms (e.g., Hagoort, 1993;Marcel, 1980). It should be noted that findings of selective access within the triplet paradigm may still be accommodated by exhaustive access models of lexical processing.…”

“…Both controls and Wernicke's aphasic subjects demonstrated selective meaning facilitation, whereas Broca's aphasics demonstrated no priming, prompting Milberg et al (1987) to suggest a disruption in the automatic accessing of lexical-semantic information. In a study of Dutch speaking aphasics with a similar ambiguity triplet priming paradigm, Hagoort (1993) used a short and long interstimulus interval (ISI) to investigate the contribution of automatic and controlled aspects of lexical processing respectively. Both Broca's and Wernicke's aphasics were able to automatically access the semantic lexicon, but had difficulties in controlled lexical-semantic processing.…”